1. Field of the Invention
This invention relates to electron beam projection systems and more particularly to methods and apparatus for replacement of electron beam projection system components such as electrodes, i.e. filaments, and cathodes.
2. Description of Related Art
U.S. Pat. No. 4,634,921 of Williams et al. for "Thermionic Cathode Heater" describes a cathode for producing and electron beam which includes a cathode heater comprising a straight wire inside a conducting circular cylinder. The cylinder in turn is located within a cathode which is heated by current through the straight wire flowing in one direction and then returning through the cylinder. The cathode is composed of a conductive material such as sintered tungsten.
U.S. Pat. No. 4,583,023 of Friedman et al. for "Electron Beam Heated Thermionic Cathode" describes an electron beam generator or the like initially heated by a suitable heating means such as an electrical hot plate to a temperature sufficient for low level electron emission from its rear surface. A sustainer voltage is applied between the cathode and the hot plate to draw electron flow of a "back electron beam" from the cathode to the hot plate through the space between them. The back electron beam heats the hot plate to a temperature sufficient to raise the temperature of the closely spaced cathode to the desired emission temperature. This heater process is ended at that point since the heating is used only initially until the desired emission temperature is reached.